1. Field of the Invention
The present invention relates to methods of dividing glass into separate pieces using a cutting liquid and to cutting liquids used for that purpose.
2. Related Art
That division of glass into separate pieces is made easier by wetting the crack formed in the glass, e.g. with water, during scribing and breaking of the glass has been known for many years in the glass blowing arts. At the same time water acts as a cooling medium for producing breaking stresses in a glass surface during scribing of the glass by means of a laser, e.g. as described in U.S. Pat. No. 6,252,197. It is already known to add a surfactant to the water, e.g. during laser cutting, (US 2003/0052098 A1) to provide a cooling liquid with improved power to penetrate the scribed line or crack formed by the laser beam. All known classes of wetting agents, i.e. anionic, cationic and nonionic wetting agents, are suitable (WO 2004/018144 A1).
It is especially important to maintain as constant as possible conditions during the dividing of the glass after scribing, when cutting extremely thin glass, e.g. for LCD applications, by means of a laser.
The glass to be divided along the scribed line is heated very rapidly by means of a laser beam during laser cutting in contrast to the scribing methods in which diamond or cutting wheels are used. The heated spots are quenched immediately after heating with the laser beam, generally by spraying the spots with a gas-water mixture. As a result, a crack is formed in the glass because of the large thermal stresses produced during quenching. The glass is broken or divided along the scribed line or crack by application of a force. The force can be applied mechanically, but it is possible to produce still more thermal stresses along the scribed line or crack by additional treatments of the glass with the laser, so that the glass breaks along the scribed line.